LOOPS 13

Quantum gravity aims at unifying Einstein's vision of space-time as a dynamical object with the realization that fundamental physics and hence space-time has to be quantum. This opens up a large variety of research questions and directions, which range from foundational physical issues having to do with the nature of space and time, to current searches for experimental signatures of quantum spacetime.

This conference, which is part of the series of Loops conferences, will present and review recent progress and highlights in loop quantum gravity and other quantum gravity approaches. We will focus mainly on background independent approaches which are approaches that do not depend on perturbation theory formulated in a classical background.

Plenary talks will highlight the most important recent developments in quantum gravity research. Afternoon (parallel) sessions are open to contributed talks and will be focussed on particular topics or subfields and give room for discussions, exchange of ideas and a critical assessment of open questions.

The conference will bring quantum gravity researchers from all over the world together and we also hope to share the excitement of quantum gravity research with participants from other research fields.

Since the standard inflationary paradigm is based on quantum field theory on classical space-times, it excludes the Planck era. Using techniques from loop quantum gravity, the theory is extended to overcome this limitations. The new framework sharpens conceptual issues by distinguishing between the true and apparent trans-Planckian difficulties and provides sufficient conditions under which the true difficulties can be overcome within a quantum gravity theory, with interesting lessons for both theory and observations.

Abhay Ashtekar, Pennsylvania State University

Promising Paths

In LQG we work in the spirit of Antonio Machado: "Traveler, there is no path; Paths are made by walking." I will present a bird's eye view of some of the paths that have emerged since Loops 11 and offer a few suggestions.

Aurelien Barrau, Universite Joseph Fourier

Some possible ways to observe consequences of loop quantum gravity

In this talk, I'll briefly review some possible observational consequences of loop quantum gravity. I will first address the issue of the closure of the algebra of constraints in holonomy-corrected effective loop quantum cosmology for tensor, vector, and scalar modes. I will underline some unexpected features like a possible change of signature. The associated primordial power spectrum and the basics of the related CMB analysis will be presented. The "asymptotic silence" hypothesis will be mentioned as a promising alternative. Then, I'll address the issue of the probability for inflation and the prediction of its duration from a new perspective. Finally, I'll present some prospect about the evaporation of black holes in LQG.

Eugenio Bianchi, Perimeter Institute

Entanglement, Bekenstein-Hawking Entropy, and Spinfoams

I review recent developments on vacuum entanglement perturbations in perturbative quantum gravity and spinfoams, and discuss their relevance for understanding the nature of black hole entropy.

Steve Carlip, University of California, Davis

Spontaneous Dimensional Reduction?

Several lines of evidence hint that quantum gravity at distances a bit larger than the Planck scale may become effectively two-dimensional. I will summarize the evidence for this "spontaneous dimensional reduction," and suggest a further argument based on the effect of vacuum fluctuations on light cones. If this description proves to be correct, it suggests an interesting relationship between small-scale quantum spacetime and the behavior of cosmologies near a spacelike singularity.

Fay Dowker, Imperial College, London

Causal Sets and the Quantum of Action

The struggle between local and global concepts in physics comes to a head in causal set quantum gravity. Local physics -- and general relativity in particular -- must be recovered in a continuum approximation if the theory is to be successful but causal sets are inherently non-local entities. I will describe a family of causal set actions labelled by dimension, each of which is nonlocal and yet, when applied to certain causal sets, approximates the Einstein Hilbert action and is therefore effectively local. I will explain why this is a source of hope that causal set theory has a continuum approximation.

Henrique de Andrade Gomes, University of California, Davis

Shape Dynamics: a status report

I will give an introduction to the theory of Shape Dynamics, and then comment on recent advances, obstacles and future projects.

Dafne Guetta, ORT-Braude College & INAF-OAR

Quantum Gravity Phenomenology with Neutrinos and high energy photons.

I review the main properties of the Gamma Ray Bursts (GRBs) as possible sources of high energy (E>TeV) neutrinos and confirmed sources of high energy (E>GeV) photons.

I discuss the possibility to use the data of neutrino telescopes, such as IceCube and the GeV-photon telescopes, such as Fermi’s LAT, for precision tests of Einstein's Special Relativity as applied to neutrinos and photons. My focus is on possible departures from Special Relativity that can be motivated by models of quantum space-time. I observe that neutrinos which one would not associate to a GRB, when assuming a classical spacetime picture, may well be GRB neutrinos if the possibility that Lorentz invariance is broken at very high energies is taken into account. I outline how future analyses of neutrino data should be done in order to systematically test the Lorentz Invariance Violation possibility. In addition I consider the possibility that Lorentz Invariance Violation might be responsible for the spectral lags that characterize the GeV signal observed for the remarkable GRB130427A.

A comparison of these features for GRBs at different redshifts provides some encouragement for a redshift dependence of the effects of the type expected for a quantum-spacetime interpretation, but other aspects of the analysis appear to invite the interpretation as intrinsic properties of GRBs.

Razvan Gurau, Universite Paris-Sud

he non perturbative 1/N expansion of Tensor Models

I will present the recently obtained non perturbative 1/N expansion of tensor models. The correlation functions are shown to be analytic in the coupling constant in some domain of the complex plane and to support appropriate scaling bounds at large N. Surprisingly, the non perturbative setting turns out to be a powerful computational tool allowing the explicit evaluation order by order (with bounded rest terms) of the correlations.

Muxin Han, Centre de Physique Theorique

Spinfoam Formulation of Loop Quanum Gravity

Recently there are a lot of progresses in developing the spinfoam formulation of loop quantum gravity. In this talk I give an overview of the subject. I introduce the formalism and the motivation of the theory, and I discuss the application of spinfoam formulation in black hole and cosmology. I also discuss the inclusion of the quantum matter fields and cosmological constant in the formalism. The inclusion of cosmological constant motivates a Chern-Simons formulation of LQG. Finally I discuss the semiclassical low-energy approximation of the spinfoam formulation, where Einstein gravity appears as the leading contribution.

Spin foam models are models for space time built from discrete chunks of quantized geometry. In the asymptotic regime the classical geometry is regained.

In the last year we have seen rapid developments in our understanding of this geometry at the level of the entire partition function. In particular it was found that the geometries that contribute to the partition function in the asymptotic regime satisfy accidental curvature constraints.

I will discuss the classic results and role of asymptotics, the recent results and their impact on the interpretation of these models.

Viqar Husain, University of New Brunswick

Scenes from polymer quantization

A regime of "polymer quantum field theory on curved spacetime" should emerge in a low energy approximation of quantum gravity based on LQG ideas. This era should be characterized by a polymer scale, and give modifications to the usual semiclassical approximation. I will describe work on gravitational collapse, cosmology, and statistical mechanics in this setting. Results include models of horizon evaporation, inflation and graceful exit without an inflaton potential, and an indication of dimensional reduction from 4 to 2.5 dimensions.

I will describe a very large class of gauge theories that do not use any external structure such as e.g. a spacetime metric in their construction. When the gauge group is taken to be SL(2) these theories describe interacting gravitons, with GR being just a particular member of a whole family of gravity theories. Taking larger gauge groups one obtains gravity coupled to various matter systems. In particular, I will show how gravity together with Yang-Mills gauge fields arise from one and the same diffeomorphism invariant gauge theory Lagrangian. Finally, I will describe what is known about these theories quantum mechanically.

Etera Livine, Ens de Lyon

Spinor and Twistor networks in Loop Gravity

I will review the reformulation of the loop gravity phase space in terms of spinor networks and twistor networks, and present how these techniques can be used to write spinfoam amplitudes as discretized path integrals and to study the dynamics that they define (recursion, Hamiltonian constraints as differential equations).

Renate Loll,Radboud University Nijmegen

Causal Dynamical Triangulations without Preferred Foliation

We introduce a generalized version of the Causal Dynamical Triangulations (CDT) formulation of quantum gravity, in which the regularized, triangulated path integral histories maintain their causal properties, but do not have a preferred proper-time foliation. An extensive numerical study of the associated nonperturbative path integral in 2+1 dimensions shows that it can nevertheless reproduce the emergence of an extended de Sitter universe on large scales, a key feature of CDT quantum gravity. This suggests that the preferred foliation normally used in CDT is not a crucial (although convenient) part of its background structure.

Alejandro Perez, Centre de Physique Theorique

Black holes in loop quantum gravity: new insights and perspectives from semiclassical consistency

I will argue that the recently introduced quasilocal framework for black hole mechanics (based on the form of the near horizon geometry of stationary black holes (BHs)) together with an additional assumption on the degeneracy of the area spectrum in quantum gravity (holography for non geometric degrees of freedom) leads to agreement between the statistical mechanical treatment of quantum black holes and standard semiclassical results in BH thermodynamics. More precisely, up to small quantum corrections, quantum black holes satisfy the following properties: Entropy is Bekenstein-Hawking entropy, and fluctuations of the horizon area are small. Moreover, under the above assumption, an explicit correspondence between the statistical mechanical treatment of the fundamental LQG degrees of freedom and the semiclassical Euclidean path integral formulation can be explicitly established.

Vincent Rivasseau, Universite Paris-Sud XI Orsay

The Tensor Track

I will present the tensorial renormalization group approach to quantum gravity and the tentative scenario it suggests for the emergence of space-time.

Carlo Rovelli, Le Centre de Physique Théorique

What have we learned so far about quantum gravity?

I try to make the point about what we know and what we do not yet know about the possibility of writing a quantum theory of gravity.

Frank Saueressig, Radboud University Nijmegen

Black holes in Asymptotically Safe Gravity

In this talk, I will briefly review the main ingredients of the gravitational asymptotic safety program before focusing on the phenomenological consequences originating from the scale-dependent couplings characteristic for the theory. In particular, I will discuss recent unexpected developments in unveiling the structure of microscopic black holes within Asymptotic Safety: in the asymptotic UV the structure of the quantum solutions is universal and given by the classical Schwarzschild-de Sitter solution, entailing a self-similarity between the classical and quantum regime. As a consequence asymptotically safe black holes evaporate completely and no Planck-size remnants are formed. The relation of these results to previous criticism that Asymptotic Safety does not reproduce the state-count of a conformal field theory will be addressed.

David Skinner, DAMTP & Institute for Advanced Study

Twistor Strings for N=8 Supergravity

The perturbative S-matrix of General Relativity has a rich and fascinating geometric structure that is completely obscured by its traditional description in terms of Feynman diagrams. I'll explain a new way of looking at four dimensional supergravity: as a string theory in twistor space. All tree-level amplitudes in the theory can be described by algebraic curves in Penrose's nonlinear graviton

Spacetime covariance in canonical quantum gravity is tied to the existence of an anomaly free representation of its constraint algebra. I will argue that establishing the existence of such a representation in the LQG context requires the consideration of higher than unit density weight Hamiltonian constraints. Smolin's weak coupling limit of Euclidean gravity, while simpler than full blown gravity , still exhibits an open constraint algebra isomorphic to that of gravity and offers an ideal testing ground for the investigation of the quantum constraint algebra of such higher density constraints. I will report on recent progress on this issue in the context of an LQG type quantization of this system. Certain features of the constructions such as the encoding of the action of the quantum constraint in terms of operator valued diffeomorphisms may play a key role in the definition of a consistent quantum dynamics for LQG.

A Shift in Time featuring the TorQ Percussion Quartet Thursday, July 25th @ 7:30pmMike Lazaridis Theatre, Perimeter Institute Loops 13 features a unique concert opportunity that integrates art with science. This musical presentation reveals a special duality between quantum gravity and sound featuring the talents of the TorQ Percussion Quartet. TorQ’s program “A Shift in Time” examines the phenomenon of time and space in a rhythmic paradigm. Each piece explores a specific music compositional device and variations surrounding it, including metric modulation, phasing, spatial aural spectra, and acoustic delay. During the conference period the TorQ Percussion Quartet will engage with our delegates and PI community and these interactions will provide inspiration for improvisational pieces for the upcoming concert. Don't miss out on this fantastic event, an evening of percussion mastery presented by the TorQ Percussion Quartet, featuring sounds from the driving rhythms of wood to the Doppler pulsations of metallic keyboard instruments. Reserve your ticket now! For more information on TorQ visit: http://www.torqpercussion.ca/For a sample of their performance, see: http://www.youtube.com/watch?v=T2AnGfFhUcg

All participants of the Loops 13 conference are encouraged to dine in Perimeter Institute’s Black Hole Bistro. The following events have been scheduled for your enjoyment.

Please come join your fellow conference participants in the bistro for dinner. There is no charge to attend this dinner.

Thursday, July 25

A reception will take place immediately following the TorQ Percussion Quartet concert. Concert attendees may enjoy a beverage and light snacks after the performance. There is no charge to attend the reception.

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Loops '13 Football Tournamenta.k.a.the 2nd edition of the Loops' mini world cup tournament

After a first edition organized during the Madrid conference during Loops' 11, the Loops' Cup is back! While the 2011 tournament was won by an international selection, we are planning to change the format of the cup; it will be organzied most likely by research topics instead of national teams (since there were not enough nationals for each country last time). We are planning to play on Wednesday afternoon (July 24) in Waterloo Park. A field has been reserved for play from 2:00 - 5:00pm. The basic setting is a round robin followed by direct elimination rounds concluded by a little final and the big final. Depending on the total number of players, teams will consist of 5-7 players and games will last between 10 and 20 minutes. In total we are hoping for 6 to 8 teams. The exact time and format (teams and game plan) will be decided over the next couple of weeks before the conference, according to the number of participants and their properties. A priori, teams will correspond to thematics:

Loop gravity & canonical techniques

Spinfoams & GFT

Cosmology & LQC

CDT & Shape dynamics

QG phenomenology

BHs & Thermodynamics of GR

Strings & CFT

Players wanting to qualify to a specific thematic team should provide a proof of research in that thematic (no need of anything formal). To register for the cup please send an email to footpiloops12@gmail.com with your name, preferred thematic(s), birth country and institution (these last two will be needed in case it is finally decided to switch back to the original national team format.) If you have other questions, please direct them to Etera Livine or Florian Girelli. There will likely be a Perimeter Institute / conference staff team if enough participants are interested. Comments and suggestions may be included in the text of your registration email or may be posted to the facebook event webpage:https://www.facebook.com/events/188604221300066/?ref=14 If you want to play, please think about bringing a white t-shirt and a black t-shirt, and appropriate footwear to play on grass. Games will be self-refereed, with ultimate decision residing with the organizers. Water and fruit will be provided.

Giovanni Amelino-Camelia, La Sapienza University of Rome

Abhay Ashtekar, Pennsylvania State University

Fernando Barbero, Instituto de Estructura de la Materia

John Barrett, University of Nottingham

James Bjorken, SLAC

Martin Bojowald, Pennsylvania State University

Robert Brandenberger, McGill University

Alejandro Corichi, Pennsylvania State University

Fay Dowker, Imperial College, London

Rodolfo Gambini, Instituto de Fisica Facultad de Ciendias

Steve Giddings, University of California, Santa Barbara

Viqar Husain, University of New Brunswick

Ted Jacobson, University of Maryland

Kirill Krasnov, University of Nottingham

Jerzy Lewandowski, University of Warsaw

Stefano Liberati, SISSA

Etera Livine, Ens de Lyon

Renate Loll, Radbud University Nijmegen

Yongge Ma, Beijing Normal University

Joao Magueijo, Imperial College, London

Alex Maloney, McGill University

Matilde Marcolli, California Institute of Technology

Guillermo Mena, Instituto de Estructura de la Materia

Djordje Minic, Virginia Tech

Daniele Oriti, Albert Einstein Institute

Roberto Percacci, SISSA

Alejandro Perez, Centre de Physique Theorique

Jorge Pullin, Lousiana State University

Martin Reuter, Johannes Gutenberg Universitat

Vincent Rivasseau, Laboratoire de Physique Théorique d'Orsay

Carlo Rovelli, Centre de Physique Theorique

Thomas Thiemann, University of Erlangen-Nuernberg

William Unruh, University of British Columbia

Joseph Ben Geloun, Perimeter Institute

Eugenio Bianchi, Perimeter Institute

Valentin Bonzom, Perimeter Institute

Bianca Dittrich, Perimeter Institute

Astrid Eichhorn, Perimeter Institute

Cecilia Flori, Perimeter Institute

Laurent Freidel, Perimeter Institute

Steffen Gielen, Perimeter Institute

Florian Girelli, Perimeter Institute & University of Waterloo

Philipp Hoehn, Perimeter Institute

Mercedes Martin-Benito, Perimeter Institute

Flavio Mercati, Perimeter Institute

Lee Smolin, Perimeter Institute

Guest Speakers: Ground transportation arrangements will be made on your behalf and instructions sent prior to your arrival. If you need transportation while attending the conference, we offer suggestions below. If flying, we suggest that you book your flight to arrive atToronto International Airport (YYZ) or the Region of Waterloo International Airport (YKF).

Boulevard Limousine (estimated travel time 1hr) The fare for Boulevard Limousine for one passenger is $118.00 to the Toronto Airport. The fare for one passenger from the Toronto Airport to Waterloo is $133.00. To make reservations, please visit their website or call 519-886-8090.

Airways Transit (estimated travel time 1hr) Airways Transit connects Toronto (Pearson), Hamilton (Munro), and Region of Waterloo International Airports with the Kitchener-Waterloo area by providing 24 hour shared ride door-to-door service. For Toronto Pearson airport we have obtained a reduced conference fare of $58.00 per person, one way, tax included. To receive the reduced fare you must book in advance and identify yourself as a LOOPS 13 delegate. To make reservations online: http://conferences.airwaystransit.com Enter booking code LOOPS 13 (enter exactly as shown) By phone 24 hours: 519-886-2121 Please identify yourself as a LOOPS 13 delegate.

Car Rentals Upon arrival in any of the terminals at Pearson International Airport there are a number of car rental agencies to choose from. Their booths are located on the arrivals level. The cost of a car rental is dependent upon the type of vehicle you would like and the length of the stay. Driving Directions

Travel forward another 200 metres, but ease over into the right-hand lane. As you go down a hill and around a curve, look for the green Perimeter Institute sign on the right hand side. The parking lot entrance is just after the sign (past the historic grist mill that sits on the edge of Silver Lake).

Turn right into the PI parking lot entrance.

If you are planning on driving to PI, please arrive 20 minutes early to allow time for you to obtain a short-term parking pass from reception and to park your car in the appropriate lot. This short-term pass will allow you to park for the duration of the conference at the Bauer Parking lot on Father David Bauer Drive across the street from the Waterloo Recreation Complex.

In LQG we work in the spirit of Antonio Machado: "Traveler, there is no path; Paths are made by walking." I will present a bird's eye view of some of the paths that have emerged since Loops 11 and offer a few suggestions.

I try to make the point about what we know and what we do not yet know about the possibility of writing a quantum theory of gravity.

A regime of "polymer quantum field theory on curved spacetime" should emerge in a low energy approximation of quantum gravity based on LQG ideas. This era should be characterized by a polymer scale, and give modifications to the usual semiclassical approximation. I will describe work on gravitational collapse, cosmology, and statistical mechanics in this setting. Results include models of horizon evaporation, inflation and graceful exit without an inflaton potential, and an indication of dimensional reduction from 4 to 2.5 dimensions.